it's a great idea indeed. Show him some videos on Youtube or in social networks,its the easiest way
Or better ask some person who directly works in some blockchain platform, they can advise you some personal companies resources
Bitcoin will be more popular and it is great idea that children knows and learn about it while they are growing. Children today are more advance than before and use different gadgets in their young age. It will be advantage to them than other that they are aware on the blockchain that has been created for them to know the use of it and make them do want they want to do. It won't be hard to teach them by let them watch on YouTube about it then answer the questions that they will ask.